1. Chop the garlic finely. Place it in a small mixing bowl and add the mustard and vinegar. Mix well with a fork. Add the herb of your choice and salt and pepper to taste. Whisking with your fork, dribble in the olive oil in a steady stream until the dressing has emulsified.
2. Put the (well dried) greens in a large glass bowl (or other appropriate serving dish) add vinaigrette and serve.
Note: If you put all the ingredients for your vinaigrette into a small glass jar with a tight fitting lid, you can just shake the jar to mix. Then, if you have dressing left over, you can refrigerate it in that jar to reuse for a few days!

You might also want to ensure that that excellent vinaigrette is evenly distributed. I like to pour a little of the dressing into the empty bowl, then swirl the completely dried greens around until they are all lightly coated. Bring the rest of your dressing to the table for anyone who feels they've been short-changed.

Have you ever made salad dressing with butter in place of the oil? To die! Also a spoon of poppy seeds or toasted sesame seeds will bump your salad to another level.

Another piece of the answer comes from the discussion in a more recent question about washing greens. If the greens are not dry, the dressing will not adhere well. And, also as Amanda says above, "made fresh" makes a difference. Unless you want bottles of dressing lining your refrigerator door, just make dressing as you make the salad, right over the bowl.

Here's my signature dressing, usually on endive/watercress/boston mixture with tomato and sourdough croutons (and avocado optionally for a dinner salad):

1 tablespoon dijon mustard
1 tablespoon balsamic or red wine vinegar (add pinch sugar if you use wine vinegar)
hard shake of oregano, grinding of pepper
Whisk this, then dribble in olive oil while whisking until you like the taste and consistency, about half a cup? I like it quite acidic myself. Then add
1 tablespoon dark sesame oil
1 tablespoon soy sauce
Makes a lot. I usually overdress the salad because I like the dressing so much.